https://youtu.be/OcziDFnhOUI?si=bjuwkFxLudahy70-

Hi Magister41. Your body can be re-trained over time. In addition to Michael's description, the whole idea behind the PLB technique is to create building up a BACK Pressure in the lungs which helps the bad air get rejected from the damaged pockets.

My therapists also emphasized giving a very forceful exhale at a double count of the intake cycle. The longer this increases over time, the better.

For mouth-breathers this may require holding the breath (or squeezing the nose) to accomplish - both very uncomfortable maneuvers. For this, you may find using a strong balloon (or even a used med inhaler canister) will help even out the process if mouth breathing is the best you can do. Check out the video below:
be Well.

Interesting question. I'm sure others will chime in with answers and may even have more technical info on it.
But.. in my opinion. I believe it will still work. Maybe not as effectively and might take a little longer. But it is just inhale through your nose for 4 seconds, hold for 4, and exhale pursued lipped long and slow for 8 seconds.
Explanation why; There is a nerve that goes from the the sinuses [Back of your nose] to your lungs that helps control our breathing reflex. By doing it in that order it helps tell your lungs when to exchange oxygen, thus improving your oxygen exchange. It gets a lot more technical than that, but that is how it was explained to me as I have a problem with Hypoxia.